Chapter 2 Notes

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University of Toronto Scarborough
Biological Sciences
Mark Fitzpatrick

Chapter 2 It is electrons, however, that determine how atoms will interact in chemical reactions About 98 percent of the mass of every living organism (bacterium, turnip, or human) is composed of just six elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Sodium and potassium, for example, are essential for nerve function; calcium can act as a biological signal; iodine is a component of a vital hormone; and magnesium and molybdenum are essential to plants (magnesium as part of their chlorophyll pigment, and molybdenum for incorporating nitrogen into biologically useful substances). Hydrogen doesnt have a neutron unless its an isotope. Most isotopes are stable. But some, called radioisotopes, are unstable and spontaneously give off energy in the form of (alpha), (beta), or (gamma) radiation from the atomic nucleus. Known as radioactive decay, this release of energy transforms the original atom. These transformations can extend even to a change in the number of protons, so that the original atom is now a different element. 60 radiation from Co (cobalt-60) is used in medical practice to kill cancer cells. The behaviour of ele
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